Your diction is simply your choice of words.
There is no single, correct diction in the
English language; instead, you choose different words or phrases for
different contexts:
To a friend
"a screw-up"
To a child
"a mistake"
To the police
"an accident"
To an employer
"an oversight"
All of these expressions mean the same thing -- that is, they
have the same denotation -- but you would not likely
switch one for the other in any of these three situations: a police
officer or employer would take "screw-up" as an insult, while your
friends at the bar after a hockey game would take "oversight" as
an affectation.
